The invention concerns a laminate body, in particular a laminate foil having the features of the classifying portion of claim 1 and a method of increasing the forgery-proof nature of a laminate body having the feature of the classifying portion of claim 22.
DE 37 38 330 A1 discloses a laser marking method for use in relation to surfaces with a pigment coating, wherein pigments of the pigment coating change their internal molecular structure and produce different colours, at different temperatures. The specific surface temperatures are produced locally with the laser radiation effect, thereby producing coloured laser markings.
DE 44 10 431 A1 describes a method with which person-related data are applied by laser marking to an identity card, wherein the identity card has a copying-protection element applied by a transfer method. In the laser marking procedure an identification in the form of a series of digits is applied, by a part of the series of digits being applied in the copying-protection element and a further part of the series of digits being applied in an adjoining region of the identity card. The laser marking effect is implemented by way of local demetallisation in the metal layer of the copying-protection element or by blackening of the treated region of the identity card.
EP 0 219 011 B1 describes a special method of laser marking of identity cards. That method provides that black markings are produced by means of the laser in different transparent layers of the card. In that way parallax images are produced in the mutually co-operating transparent layers.
GB 2 240 948 A also describes laser marking of identity cards. Here laser marking is produced by the removal of different coloured layers. The laser marking which is produced by that procedure appears in the form of a coloured marking.
DE 41 31 964 A1 describes laser marking of a laminate foil with a metal layer and a hologram structure. The marking operation is effected by region-wise blackening and removal of layers.
EP 0 420 261 A2 discloses various measures for increasing the forgery-proof nature for systems with hot stamping foils with a hologram structure. Described therein inter alia is that laser-induced markings are produced by laser treatment in the hologram structure or in other lacquer layers of the foil. Another method of individualising foils with a hologram structure, which can be applied additionally or alternatively, is described, providing for the use of an individualising embossing stamp which imparts an individualised external contour to the hologram structure. A disadvantage with the described individualisation methods is that it is not readily possible to detect whether the situation involves a forgery, on the basis of the foil applied to the substrate, without referring to a comparative pattern.
The production of multi-colour markings in coatings is known from WO 96/35585 and WO 94/12352, while the production of single-colour markings is known from EP 0 327 508, EP 0 190 997 and DE 37 38 330. The following applies in that respect:
WO 96/35585 discloses various configurations of plastic bodies, more specifically solid bodies or coatings, which each contain a mixture of various pigments. In the various embodiments set forth by way of example the pigment mixture is composed of three pigment components, more specifically a yellow pigment, a magenta pigment and a cyan pigment. Colour marking is effected on the plastic body by laser treatment. The colour marking occurs due to bleaching of the pigments by means of the laser treatment. The laser conditions are respectively adjusted specifically with a variation in the wavelength in order to obtain given colours. The respective specific wavelength used is previously ascertained by light absorption measurements in regard to the pigments, more specifically in each case the absorption wavelength at the absorption maximum of the pigment is ascertained. Each case involves using pigments which have only one single absorption maximum. That is intended to guarantee that, in the laser treatment, the result obtained is a colour which corresponds to the colour of the laser light and the duration of the laser treatment and the intensity of the laser light for each colour can be of the same value. In the described embodiment with a pigment mixture comprising yellow pigment, magenta pigment and cyan pigment, violet laser light at a wavelength of 430 nm, blue laser light at a wavelength of 470 nm, yellow laser light at a wavelength of 575 nm and laser light, referred to as orange, at a wavelength of 650 nm, are used for the laser treatment. That is intended to produce different colour markings on the plastic body by means of the laser treatment by virtue of suitable adjustment of the laser wavelength, with the laser conditions being otherwise the same. The colours are produced by complex mixing of the pigments which at the same time are bleached at the respective laser wavelength. A method of producing as far as possible all colours with a limited number of pigments is not specified.
It is also known from WO 94/12352 to produce bright colour markings on a plastic body which contains a pigment mixture and which can be in the form of a solid body or a coating, by laser treatment using different wavelengths. The coloration effect is implemented by the pigments changing their colour due to colour transposition in the laser treatment. The laser conditions are randomly selected in each case. A method of deliberately and specifically producing any colours is not specified. In addition the number of colours produced in that way is greatly limited.
EP 0 327 508 discloses a method in which a laser-sensitive dyestuff A and a laser-insensitive dyestuff B are contained in two separate mutually superposed lasers or in a common layer and are bleached by laser treatment of the dyestuff A while the laser-insensitive dyestuff B is not bleached or is only slightly bleached. The laser treatment results in the production of a colour marking, but only a single-colour marking, that is to say at a maximum a two-colour image. The method does not provide for any variation in the laser conditions to produce different colours.
EP 0 190 997 B1 discloses a method in which a plastic plate or a plastic layer in the form of a coating on a metal plate portion contains an additive which can be coloured under the effect of laser treatment, more specifically by colour transposition from one colour into another or by conversion into black. Colour markings involving different colours are not possible in that case.
EP 0 416 664 B1 discloses producing black markings by laser markings in plastic bodies or foil layers. The markings are produced by laser-governed blackening of the laser-sensitive component molybdenum sulphite contained in the plastic material.
It is known from DE 195 22 397 A1 to produce light marking or labelling by laser treatment of plastic layers containing pigments. That is effected by laser bleaching of the pigments involved.
EP 0 537 668 and DE 81 30 861 U1 disclose region-wise removal of layers in the layer structure of transfer foils by laser treatment in order in that way to produce markings.
In addition it is known for example from EP 0 741 370 B1, DE 43 33 546 A1 or U.S. Pat. No. 4,911,302 to produce markings by laser-induced melting of the material, by virtue of laser treatment of laminate bodies, in order then to transfer those markings while still in the molten condition on to another body.